首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4970篇
  免费   1118篇
  国内免费   1222篇
测绘学   422篇
大气科学   836篇
地球物理   1334篇
地质学   2721篇
海洋学   668篇
天文学   293篇
综合类   437篇
自然地理   599篇
  2024年   17篇
  2023年   69篇
  2022年   206篇
  2021年   258篇
  2020年   194篇
  2019年   270篇
  2018年   294篇
  2017年   264篇
  2016年   272篇
  2015年   255篇
  2014年   293篇
  2013年   322篇
  2012年   321篇
  2011年   345篇
  2010年   326篇
  2009年   308篇
  2008年   279篇
  2007年   254篇
  2006年   227篇
  2005年   228篇
  2004年   195篇
  2003年   193篇
  2002年   228篇
  2001年   224篇
  2000年   200篇
  1999年   199篇
  1998年   173篇
  1997年   153篇
  1996年   134篇
  1995年   91篇
  1994年   96篇
  1993年   90篇
  1992年   69篇
  1991年   52篇
  1990年   44篇
  1989年   31篇
  1988年   30篇
  1987年   22篇
  1986年   22篇
  1985年   16篇
  1984年   14篇
  1983年   9篇
  1982年   6篇
  1981年   5篇
  1980年   3篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1958年   1篇
  1954年   3篇
排序方式: 共有7310条查询结果,搜索用时 31 毫秒
991.
�봨����ǰ��ɽ�����ݴ��ĵؿ��˶�   总被引:3,自引:0,他引:3  
????GPS?????????“???????”?????????????????????????????????????????????????????????????????????NW???????????????????????????????????????????????5~6????????????????????2???????????????????????NW????NEE????Щ????????????????????GPS?????????????????????£????????????????????????????????????????????????????????????????α???????????仯?????  相似文献   
992.
The eutrophication, hypoxia and coastal acidification are attracting more and more attention. In this study, inorganic carbon parameters, including dissolved inorganic carbon (DIC), total alkalinity (TA) and calculated partial pressure of CO2 (pCO2), obtained from a summer cruise in August, 2009, were used to investigate their integrated response to biological processes accompanying the oxygen depletion in the areas off the Changjiang Estuary. According to the observations, the typical hypoxia occurred in the bottom water just outside the Changjiang Estuary with Dissolved Oxygen (DO) lower than 2.00 mg L?1. The biological uptake in the surface water and the decomposition of organic matter in the bottom water were fully coupled with each other. The high concentration of Chl_a (Chl_a = 10.9 μg L?1) and DO (9.25 mg L?1), profoundly decreased DIC concentration (1828 μmol kg?1) and elevated pH (8.42) was observed in the surface water. The correspondingly increased DIC and depletion of oxygen were observed in the bottom water. The semi-quantitative analysis proved that the locally-produced phytoplankton, determined by primary productivity, was deposited to the bottom and contributed about 76% of total amount of the organic carbon decomposition in the bottom. However, in the bottom hypoxia (DO = 2.05 mg L?1) area observed in the Southern Zhejiang coastal water, the responding patterns of inorganic carbon parameters deviated from the previous one. The expanding of Changjiang Diluted Water (CDW), the adding of Hangzhou Bay water (with high DIC concentration) and Coastal Current together modify the DIC background value in this area, and the local degeneration and upwelling process may also help to offset the local DIC removed by net biological uptake in surface water. In addition, when the mixing occurring in autumn, which may break the summer stratification, the excess release of high DIC in the bottom water to the subsurface water could have an important influence on coastal acidification and the CO2 uptake capacity in this area.  相似文献   
993.
Cytochrome P450 (CYP) superfamily is one of the membership largest and function most diverse protein superfamily recogniozed among living beings. Members of this superfamily were further assigned to different families and subfamilies based on their amino acid similarities. According to their phylogenetic relationships, the CYP genes which likely diverged from common ancestor gene and may share common functions were grouped into one clan. Widely distributing scallops are a group of the most conspicuous bivalve; however the studies on their CYP is acarce. In this study, we searched the genome and expressed sequence tags of Zhikong scallop (Chlamys farreri) for CYP genes. In total, 88 non-redundant CYP were identified, which were homed in 13 CYPs gene families. Phylogenetic analysis divided these genes into 4 CYP clans. As in deuterostomes, Clan 2 was the largest, which contained 33 genes belonging to CYP1, CYP2, CYP17 and CYP356 families. Clan 3 contgained 19 genes belonging to CYP3, CYP5 and CYP30 families. Clan 4 contained 23 genes, all belonging to CYP4 family. The mitochondrial CYP clan contained 9 genes belonging to CYP10 and CYP24 families. In comparison, protostomes (C. farreri, D. pluex, D. melanogaster) contained more CYP genes than deuterostomes (S. purpuratus and vertebrates) in Clan 2 but less genes in Clan 3 and Clan 4. Our findings will aid to deciphering CYP function and evolution in scallops and bivalves.  相似文献   
994.
Zhikong scallop(Chlamys farreri) is an important maricultured species in China.Many researches on this species,such as population genetics and QTL fine-mapping,need a large number of molecular markers.In this study,based on the expressed sequence tags(EST),a total of 300 putative single nucleotide polymorphisms(SNPs) were selected and validated using high resolution melting(HRM) technology with unlabeled probe.Of them,101(33.7%) were found to be polymorphic in 48 individuals from 4 populations.Further evaluation with 48 individuals from Qingdao population showed that all the polymorphic loci had two alleles with the minor allele frequency ranged from 0.046 to 0.500.The observed and expected heterozygosities ranged from 0.000 to 0.925 and from 0.089 to 0.505,respectively.Fifteen loci deviated significantly from Hardy-Weinberg equilibrium and significant linkage disequilibrate was detected in one pair of markers.BLASTx gave significant hits for 72 of the 101 polymorphic SNP-containing ESTs.Thirty four polymorphic SNP loci were predicted to be non-synonymous substitutions as they caused either the change of codons(33 SNPs) or pretermination of translation(1 SNP).The markers developed can be used for the population studies and genetic improvement on Zhikong scallop.  相似文献   
995.
为寻找墨西哥湾扇贝中对其闭壳肌重量影响最显著的形态学特征,在整个扇贝的生长过程中,每一个月测一次壳高(mm)、壳宽(mm)、铰合线长(mm)、体质量(g)和闭壳肌质量(g),每一轮的样本采集量为60,通过通径分析研究这些形态学特征对闭壳肌质量的影响。结果显示,根据各形态学特征对闭壳肌质量的直接的、间接的、总路径的贡献,发现体质量的影响是最显著的(p<0.01),其他的形态学特征如壳高、壳宽和铰合线长对于闭壳肌生长既不限制也不促进。  相似文献   
996.
武汉九峰地震台超导重力仪观测分析研究   总被引:9,自引:1,他引:8       下载免费PDF全文
连续重力观测和GPS的技术结合能够监测到物质迁移和地壳垂直形变之间的量化关系.和相对重力测量以及绝对重力测量技术相比,其避免了时间分辨率和观测精度低,无法精细描述观测周期内的物质迁移过程问题.本文利用武汉九峰地震台超导重力仪SGC053超过13000 h连续重力观测数据;同址观测的绝对重力仪观测结果;气压数据;周边GPS观测结果;GRACE卫星的时变重力场;全球水储量模型等资料,采用同址观测技术、调和分析法、相关分析方法在扣除九峰地震台潮汐、气压、极移和仪器漂移的基础上,利用重力残差时间序列和GPS垂直位移研究物质迁移和地壳垂直形变之间的量化关系.结果表明:在改正连续重力观测数据的潮汐、气压、极移的影响后,不仅准确观测到2009年的夏秋两季由于水负荷引起的约(6~8)×10-8m·s-2短期的重力变化.而且在扣除2.18×10-8(m·s-2)/a仪器漂移和水负荷的影响后,验证了本地区长短趋势垂直形变和重力变化之间具有一致的负相关性规律.同时长趋势表明该地区地壳处于下沉,重力处于增大过程,增加速率约为1.79×10-8(m·s-2)/a.武汉地区重力梯度关系约为-354×10-8(m·s-2)/m.  相似文献   
997.
A nonlinear finite element model for earthquake response analysis of arch dam–water–foundation rock systems is proposed in this paper. The model includes dynamic dam–water and dam–foundation rock interactions, the opening of contraction joints, the radiation damping of semi‐unbounded foundation rock, the compressibility of impounded water, and the upstream energy propagating along the semi‐unbounded reservoir. Meanwhile, a new equivalent force scheme is suggested to achieve free‐field input in the model. The effects of the earthquake input mechanism, joint opening, water compressibility, and radiation damping on the earthquake response of the Ertan arch dam (240 m high) in China are investigated using the proposed model. The results show that these factors significantly affect the earthquake response of the Ertan arch dam. Such factors should therefore be considered in the earthquake response analysis and earthquake safety evaluation of high arch dams. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   
998.
我们收集了紫坪铺水库区域台网记录到的2004年8月16日至2008年5月12日汶川地震前发生在震中区及附近区域的486个小震震源机制资料,运用碎裂分析法对这些震源机制数据进行分析,获得了汶川地震前3年多时间内震源区应力水平随时间的演化过程.结果显示,强震发生前震源及附近区域约在2007年6月发生了应力突变,出现了2个应力异常高值区,其形成过程同时伴随着龙门山中央断裂的应力水平降低,最终强震发生在高应力区和低应力区之间的应力梯度带上.汶川地震前应力状态的演化过程,类似于实验研究中出现的非均匀断层失稳前的地震成核现象,符合地震成核的宏观表现.巴颜喀拉块体的南边界-鲜水河断裂的短基线测量也显示出,在同一时间段鲜水河断裂南段由左旋滑动转为异常的右旋错动,反映了汶川强震前整个巴颜喀拉块体有向东加速运动的异常过程.  相似文献   
999.
依兰-伊通断裂带地表温度变化分析   总被引:1,自引:0,他引:1       下载免费PDF全文
任雅琼  陈顺云  马瑾 《地震学报》2012,34(5):698-705
GPS结果显示,2011年3月11日日本MW9.0大地震引起了我国东北地区的拉张活动增强,其中,依兰——伊通断裂带最显著.这个变化在温度场中是否也有所响应是一个值得探讨的问题,也是一个利用地表温度进行现今构造活动探索的机会.本文利用2000——2011年的中分辨率成像光谱仪(MODIS)地表温度产品对东北地区地表温度进行了分析,以去除稳定年周期变化的年变残差作为研究对象, 通过空间和时间分析,排除地形、纬度、气象等干扰因素的影响,寻找与构造活动相关的热信息.结果表明, 2001年初和2010年初依兰——伊通断裂北段曾经出现了显著的降温现象,且降温过程持续约两个月.通过气象资料分析,初步认为上述现象并非由气象因素引起.这与GPS远场同震位移结果所显示的依兰——伊通断裂带在日本地震后出现相对比较明显的张性应变相吻合. 初步认为上述降温现象与依兰——伊通断裂的拉张增强有关.   相似文献   
1000.
潮汐触发地震研究进展综述   总被引:2,自引:0,他引:2  
  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号